# Build Backend

> Build or modify backend APIs, services, jobs, persistence, and integrations while preserving contracts, authorization, data integrity, and failure behavior. Use for server-side features, database changes, background processing, backend defects, and service refactors; do not use for frontend-only or infrastructure-only work.

- Skill: `hashgraph-online-awesome-codex-plugins/build-backend` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add hashgraph-online-awesome-codex-plugins/build-backend`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hashgraph-online-awesome-codex-plugins/build-backend/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: hashgraph-online (https://skillmd.com/u/hashgraph-online-awesome-codex-plugins)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/hashgraph-online-awesome-codex-plugins/build-backend

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# Build Backend

## Domain contract

- Trace changed behavior from input through validation, authorization, domain
  logic, persistence, side effects, and response mapping.
- Preserve published contracts unless the request explicitly changes them.
- Enforce authorization at a trustworthy server-side boundary.
- Validate untrusted input before domain or persistence operations.
- Keep multi-write operations atomic where partial state would violate invariants.
- Design external calls for timeouts, retries, idempotency, and duplicate delivery where applicable.
- Do not query or mutate production data without explicit authorization.
- Do not fabricate migration, framework, or API behavior; verify version-sensitive details.
- Avoid broad service abstractions that are used once.

## Execute and verify

Read [references/contracts-and-data.md](references/contracts-and-data.md) when the task changes a public API, schema, transaction, job, or integration.

Implement the smallest change at the owning layer. Cover success, invalid
input, authorization, and material failure paths. Prefer:

```text
reproducing/focused test → contract/integration test → type/lint → build
```

For migrations, validate forward behavior and document rollback or roll-forward strategy.